Carbon black is widely used in the fields of rubber, plastics for its properties in enhancement, function giving, improvement of processability and increment effect. Carbon black is rarely used in powder form or in grain form but in even dispersion among solid substances such as polymer matrix as rubbers, plastics or fibres, or liquid substances such as water or organic solvents. But the performance of carbon black is limited for the reason that carbon black particle is difficult to disperse evenly in polymer matrix, water or organic solvents for its specific surface area is very large so as to coagulating easily, and carbon black as inorganic filler is difficult to be compatible with organic substances such as polymers or solvents. In another aspect, along with rapid development of the nano-technology and the information technology, the requirements of carbon black are growing on its dispersion in polymer matrix, water or organic solvents and its compatibility with polymer matrix, water or organic solvents.
Sometimes carbon black is required to be modified to make full use of its properties or to improve the performance of carbon black/polymer composite or carbon black dispersion such as coatings. Methods of surface modification on carbon black which are well known include oxidation, surfactant treatment, polymeric dispersant treatment and surface grafting modification, of which the surface grafting modification is the most effective way.
Carbon black surface grafting modification which has developed in recent 40 years is an important means of chemical modification to improve the dispersibility and compatibility of carbon black. According to previous research results, it was found that surface grafting modification on carbon black may improve its dispersibility in polymer matrix or organic solvents and compatibility among dispersive mediums, may give it various functions such as photosensitivity, heat sensitivity, gas sensitivity, biological activity, crosslinking ability, hydrophilicity and lipophilicity, and may improve the performance of its composites in mechanical property, electric property, optical property and anti-electromagnetic radiation property. Therefore, the grafting modification on the surface of carbon black has been a concern of the research of rubber industry.
The research on grafted carbon black launched in 50s' of twentieth century, of which the subject concerns the mechanism of rubber reinforcement with carbon black. After 40 years' research, various methods of the surface grafting modification on carbon black has been developed, which can be classified into 3 types as follows:
(1) grafting onto the surface of carbon black: capturing the increasing polymeric chains by free radicals, anion radicals or cation radicals on the surface of carbon black and accordingly connecting them to the surface of carbon black (as disclosed in JP Sho 42-22047, Sho 44-3826, Sho 45-17248, Sho 46-26970, Hei 6-263830, U.S. Pat. Nos. 3,557,040, 4,530,961, etc);
(2) grafting from the surface of carbon black by polymerization: forming peroxidating radicals on the surface of carbon black by introducing active radicals thereon or by treatments such as discharge, ultraviolet treatment, ozonization, to initiate polymerization of monomer compound(s) as disclosed in JP Hei 6-25573, JP publication No. 2003-64279, 2003-41149, etc in which the polymerization can be divided into 3 types: free radical polymerization, anion polymerization, cation polymerization.
(3) carbon black reacting with functional polymeric compound(s): functional groups on the surface of carbon black reacting with functional polymeric compound as disclosed in JP Hei 2-24868, JP Hei 6-27269, JP publication No. 2000-154327, U.S. Pat. No. 5,952,429, etc. The reaction can further be divided in to 2 types: the reaction between active carbon black and polymeric compound(s) having hydroxyl group(s) or amino group(s), or the reaction between carbon black having carboxyl group(s) or phenolic hydroxyl group(s) on its surface with functional polymeric compound with active terminal(s).
It attracts attention from many manufactures for carbon black is suitable for ink, coating, nanophase materials and gas sensors after surface modification by polymer grafting. But there are certain defects existing in all these surface grafting reaction of carbon black. First, all the 3 types of above mentioned grafting modification on the surface of carbon black are performed in solution system, which may result in negative effects such as unfavorable for scale production, too costly, easy to pollute environment. Second, it's uneasy to control the structure of the modification layer of carbon black, whether directly grafting of polymeric chains onto the surface of carbon black or polymerizing of monomers which have been grafted onto the surface of carbon black. When directly grafting of polymeric chains onto the surface of carbon black, the grafting ratio is low because of the comparatively low reactivity and great steric hindrance of polymeric chains; in another aspect, when polymerizing of monomers which have been grafted onto the surface of carbon black, the processes of synthesis take more steps and the molecular weight of grafting polymer is hard to control in spite of higher grafting ratio. Though the reaction of carbon black and polymer in method (3) may graft specified polymer and can easily control the molecular weight and the chain number of grafted polymer on the surface of carbon black, there are limitations that, the polymer which can react with carbon black is limited to polymer having hydroxyl group, amino group or epoxy group, and the carbon black is limited to channel black having more oxygenic functional group on the surface instead of dissatisfying furnace black having less oxygenic functional group on the surface which is the main part of carbon black (about 90%). Third, all kinds of grafting modification of polymer are preformed in solution system, unable to obtain monodispersive primary particles, and even supersonic wave can not destroy the aggregate structure.
To sum up, it's hard to obtain monodispersive nanophase carbon black which can disperses evenly in polymeric matrix, water or organic solvents following the prior art.
After summary of all the problems above, the invention is brought forward. The objects of this invention are, to provide a nanophase carbon black produced by in situ grafting with organic compound(s), having good dispersibility in polymer matrix or organic solvents and good compatibility with dispersive mediums, whose size can be strictly controlled and able to form a stable dispersion in polymer matrix or organic solvents; to provide a synthesis method which is simple, cheap and pollution-free; and to provide articles made therefrom.